(1) Field of the Invention
This invention relates to a method for abandoning (in place) used underground storage tanks, which have contained gasoline or other flammable liquids, in an expeditious, safe, and environmentally acceptable manner.
(2) Description of the Prior Art
Storage tanks which have stored flammable liquids must be handled with extreme care when abandoned, removed, moved, or stored. This is particularly true of underground storage tanks at service stations which are most frequently used for the storage of motor fuel and for the storage of other flammable or combustible liquids such as crankcase drainings (which may contain some gasoline).
The conventional practice for the abandonment, removal, storage, placing temporarily out of service, and sale of used underground tanks which have contained gasoline or other flammable liquids is that which is set forth as operating procedures in API (American Petroleum Institute) Bulletin 1604, entitled "Recommended Practice for Abandonment or Removal of Used Underground Service Station Tanks," which teaching is incorporated by reference herein.
The importance of the prevention and detection of product leakage from petroleum storage and dispensing systems has been attested recently by Congressional action banning future underground installations of bare metal tanks. In addition, Congress has mandated identification of specified bare metal (all steel) underground storage tanks, testing said tanks for leakage, and, ultimately, removing or abandoning faulty tanks.
The safe removal of underground storage tanks may be required if it appears that a significant amount of product (a regulate substance) has leaked from it. Of course, in view of the amount of excavation required, removal is usually a very labor intensive process and, therefore, very expensive. Upon removal of all flammable liquid which can be pumped out of the tank, excavation down to the top of the tank is necessary to remove the fill tube and disconnect the fill, gauge, product, and vent lines. The open ends of lines which are not to be used further are plugged or capped. All tank openings must be temporarily plugged, excavation is completed, and the tank is removed, which involves a heavy duty crane. Since the tanks can no longer be re-used as is, they normally are cut up and sold as scrap iron. However, since it is difficult to completely remove all hazardous material (or regulated substance) from the scale or sediment in the tank, it is becoming more and more difficult to find salvage yards willing to receive such "scrap" and assume responsibility for accounting for these materials.
When abandonment of the underground storage tank is an available option, it also is a costly, labor intensive process, as conventionally practiced. As in removal, upon pumping out all flammable liquid which can be pumped out, excavation down to the top of the tank is required. The fill (or, drop) tube is removed, and the fill, gauge, and product lines are disconnected. The vent line, however, remains connected until the tank is filled to permit emission of flammable vapors. Upon removal of remaining regulated substances, one or more large holes must be made in the tank top. Of course, if any flammable vapors remain in the tank, the manner in which such a hole is made can present an explosion hazard. For instance, API Bulletin 1604 suggests making the hole with a couple of blows from a backhoe. This could, however, create sparks and ignite any flammable gases. Also, an explosion hazard is presented if the hole is made with a cutting torch.
The hole, or holes, is provided for the introduction into the tank of a suitable, solid, "inert" material. Since the tank is being abandoned in the ground, it must be filled to avoid caving in at a later date upon deterioration of the metal tank walls. The materials employed to date for this purpose are sand, sand and earth fill, and cement. Of course, with any of these materials it is almost impossible to achieve a complete fill in view of the rounded tank top. Sand is introduced dry as long as it flows freely, but it tends to pile and form a cone at the point of introduction. When the cone nears the tank top, the API recommended practice is to wash the sand into the tank with a nominal amount of water, causing it to puddle and flow to the ends of the tank. In order for this water to drain from the tank, several holes are driven into the bottom of the tank prior to introduction of the fill material. This presents two concerns. First, the use of large amounts of water should be avoided since the tank might be filled with water before it is filled with sand. And, second, in the event all of the regulated substance was not effectively removed from the tank, this procedure actually causes the release of the hazardous substance into the groundwater system, which is what the procedure purports to prevent. More nearly complete filling is suggested by first filling the tank with sand to approximately 80% capacity, mixing soil and water to make a free-flowing mud, and finally pouring the mixture into the tank opening and puddle. The third conventional alternative fill material, cement (with or without aggregate) due to its thixotropic consistency may be even more difficult to use and achieve a near complete fill. When the tank is filled to the greatest possible extent, the vent line can be disconnected and capped. Finally, the excavated area above the filled tank is filled in and smoothed over, which may involve pouring a new concrete surface.
The above discussed conventional techniques for abandoning underground storage tanks to place them in a condition such that they may never be re-used present a number of disadvantages. Often, in order to facilitate the flow of the fill material through a hole in the top of the tank, a make-shift hopper may be employed. This hopper is usually constructed of sheet metal. The movement of sand particles against the metal hopper on their way into the tank may cause a build-up of static electricity which could result in a spark entering the tank, risking a chance of an explosion if any flammable vapors remain. Also, it may be possible to vacuum out sand fill, repair the fill hole, reconnect the disconnected and capped lines, and re-use the tank. In the event that an abandoned tank had to be removed at a later time, either to comply with regulatory authority or to permit a specific land use, a tank of even average size (.about.10,000 gallons) filled with sand, sand and earth fill, or concrete would require an extremely heavy duty crane to lift it out of the ground. Once removed, disposal of the filled tank becomes an even bigger problem than it is for an empty tank. These concerns are in addition to the costs of such abandonment techniques referred to above.